Abstract
Objective
The objective of this study was to evaluate the effect of irradiation time and specimens thickness on the polymerization kinetic and variation in micro-mechanical properties of two commercial resin-based composites (RBCs) based on radical amplified photopolymerization (RAP) technology™, and to compare them with four camphorquinone (CQ)/amine-based RBCs.
Materials and methods
The materials were analysed by assessing the polymerization kinetic and the degree of cure (DC) at 0.1 mm and 2 mm depth during 5 minutes after photoinitiation, after curing for 10 s, 20 s and 40 s (Elipar Freelight2). The variation in micro-mechanical properties (Vickers hardness (HV), indentation modulus (E), and depth of cure (DOC)) was assessed in 100 μm steps on 6-mm-high specimens irradiated as above and stored in the water for 24 h at 37 °C.
Results
The results were statistically compared using one-way ANOVA with Tukey HSD post hoc test (α = 0.05) and a general linear model. The parameter material exerted the strongest effect on DC (partial eta-squared η p 2 = 0.83), followed by irradiation time (η p 2 = 0.27), and depth (η p 2 = 0.09). The polymerization kinetic, well described by an exponential sum function, showed in all materials a faster decrease in carbon–carbon double bonds at 0.1 mm than at 2 mm depth. The materials based on RAP achieved the highest DC values and a faster polymerization at both depths. The irradiation time exerted the strongest effect on the mechanical properties (DOC, η p 2 = 0.96; HV, η p 2 = 0.89; E, η p 2 = 0.86), followed by depth (HV, η p 2 = 0.63; E, η p 2 = 0.54) and material (HV, η p 2 = 0.40; E, η p 2 = 0.67). At the most favorable curing conditions (40 s, surface), the mechanical properties of the analyzed materials varied between 11.38 (0.80) GPa in Estelite® Sigma Quick and 20.80 (1.42) GPa in Estelite® Posterior for E, and between 74.33 (3.56) N/mm2 in Tetric EvoCeram® and 120.71 (6.24) N/mm2 in Estelite® Posterior for HV.
Conclusions
RAP-initiated material demonstrated a higher increase in DOC with prolonged irradiation time than the analyzed CQ/amine based materials.
Clinical relevance
An irradiation time of 20 s is also recommended for RAP-initiated RBCs.
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Acknowledgments
The measurements of the mechanical properties in this study were supported in part by the company Tokuyama-Dental.
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Ilie, N., Kreppel, I. & Durner, J. Effect of radical amplified photopolymerization (RAP) in resin-based composites. Clin Oral Invest 18, 1081–1088 (2014). https://doi.org/10.1007/s00784-013-1085-1
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DOI: https://doi.org/10.1007/s00784-013-1085-1